We propose studies characterizing signal transduction systems that are substrates for actions of drugs of abuse with a particular focus on 3 areas: 1. Nitric Oxide (NO) signaling in neurotoxicity, 2. Heme oxygenase and its products carbon monoxide (CO), bilirubin and iron, 3. Glyceraldehyde-3-Phosphate Dehydrogenase (GAPDH) as a mediator of neurotoxicity. For NO, our principal concerns are targeting of neuronal NO synthase (nNOS) and nitrosylation. We have identified Dexras1 as a novel member of the RAS family which is a physiologic target of nNOS coupled to Capon. We will characterize the physiologic role of Dexras1 by evaluating its regulation by glucocorticoids, characterizing Kalirin as a protein we recently discovered to bind Dexras1 and possibly to function as a guanine nucleotide exchange factor for Dexras1. Based on a novel technique we recently developed to monitor S-nitrosylation, we will evaluate a series of proteins that appear to be physiologic targets of S-nitrosylation. We hope to elucidate the roles of HO products in neurotoxicity and neurotransmission. We are evaluating regulation of H02 by phosphorylation, extending our initial discoveries that bilirubin is a physiologic neuroprotectant based on our recent insights that it acts catalytically through biliverdin reductase and exploring in detail interactions of NO and CO as co-neurotransmitters. We have obtained evidence that GAPDH translocation to the nucleus is an important event in various forms of cell death and have characterized evidence of molecular mechanisms underlying this translocation. We will attempt to clarify just how GAPDH acts as a sensor of oxidated stress, especially stress involving NO. Based on our discovery that GAPDH facilitates the nuclear translocation of Huntingtin, we will study molecular mechanisms whereby GAPDH influences Huntingtin neurotoxicity.